ZURICH (Reuters)—Uranium glass occupies a little-known niche in the collectables world, whose members appreciate its soft color and distinctive glow, which comes from the uranium added as the glass was created.

The pieces shown here come from the collection of Peter Marti and Markus Berner, who trade in antique glass at a small shop downstairs from their flat in Wangen an der Aare, a town in Switzerland. They discovered the glass about 15 years ago at a Swiss flea market and have been collecting ever since.

Like many uranium glass collectors, they are especially drawn to pearline, which was created by several companies, mostly in Britain, from the end of the 19th century into the 20th.

Yellow pearline is called vaseline, because the shade is similar to the color of petroleum jelly —until it’s exposed to ultraviolet light, when it glows a bright green.

The glass is slightly radioactive, enough to register on Geiger counters. But the levels are about the same as electrical appliances like microwave ovens emit, so they represent no threat to health.